Nowadays, the power needs of a system have become a key criterion for evaluating its performances. Indeed, higher energy consumption leads to greater costs and added complexity. Quite often, electricity generation might also damage the environment through e.g. greenhouse gas emissions, radioactive waste or other nuisances. These reasons create a strong demand for reducing the energy consumption of street lighting systems.
During the last decade, new lighting technologies such as LEDs (light-emitting diodes) have been successfully used in this domain. However, the high price of LEDs partially counterbalances the benefits provided by their lower energy consumption.
The lower energy consumption for an equivalent lighting level is not the only advantage of the LED technology. In particular, their ability to be switched on and off almost instantaneously, and the absence of any necessary dead time or cooling-off period between being switched off and on again stand in clear contrast to other lighting technologies such as sodium lamps. The additional flexibility offered by this advantage can be used to further decrease the global energy consumption of lighting systems, by adapting light generation more closely to actual demand.
A number of street lighting control methods and devices have been proposed to take advantage of this higher flexibility of some lighting technologies such as LED lighting to decrease global energy consumption of street lighting systems. Using sensors such as induction loops, infrared sensors, radar, etc. to detect the presence of road users, such control methods and devices turn the lighting on only when a road user may require it. By “road user” it is understood, in the present context, any person or vehicle travelling or momentarily stopped on a transportation pathway.
For instance, in the British patent application GB 2 444 734 A, a street lighting method is disclosed which comprises the steps of detecting speed and direction of travel of a road user on a first road segment, issuing a lighting command for said first road segment, and propagating a signal comprising said speed and direction of travel data of the road user through a series of adjacent road segments starting from the first road segment. However, this disclosure fails to specify how these speed and direction of travel data are then used, and does not provide any means to further optimize the light output over the individual road segments.
In the international patent application WO 2011/055259, a street lighting method is disclosed which comprises the steps of detecting a road user on a first road segment, and activating the lighting on another road segment following a previously calibrated temporal relationship. This disclosure, however, does not specify how to adapt the method to road users with greatly different speeds, or to different types of road users, such as motor vehicles and pedestrians.
Finally, in the Canadian patent application CA 2 692 187, a street lighting method is disclosed wherein a signal comprising speed and direction of travel data of a road user is propagated to a series of adjacent road segments starting from the road user's road segment over a distance not greater than a maximum distance calculated as a function of said speed and direction of travel of the road user. However, this disclosure does not specify how to adapt the lighting level to, for instance, variable traffic conditions.